Landslides

Studies of areas affected by large slope movements, stability analysis and determination of the work necessary to stabilize the movement. Instrumentation and auscultation of the terrain

Study and stability analysis of areas prone to generating surface landslides. Calculations of pressures of earthworks and proposal of protections

Studies of areas affected by large slope movements, with cartoDetailed graphing of instability indicators, and stability analysis using specific software to determine the work required for movement stabilization. Instrumentation and auscultation of the ground using piezometers, extensometers and inclinometers.

Study and analysis of the stability of areas prone to generating superficial landslides, work with the software expressly designed to carry out these works, and determination of stabilization works (or limitation of excavations) to prevent this type of mass movements. Calculations of pressures of earthworks and proposal of protections.

The term "landslide" describes a wide variety of processes that result in the downward and outward movement of slope-forming materials, including rock, soil, artificial fill, or a combination of these. Materials can be moved by falling, knocking over, sliding, expanding, or flowing. The whole topic of torrential flows and landslides are dealt with in other places on this website.

The different types of landslides can be differentiated by the type of material that is treated and by the mode of movement. A classification system based on these parameters is shown in the following figure. Other grading systems incorporate additional variables, such as speed of movement and the water, air, or ice content of the detached material.

Although landslides are mainly associated with mountainous regions, they can also occur in bas-relief areas. In low-relief areas, landslides occur in excavations for buildings and roads, in the margenes of the rivers due to erosion/scourage, embankment collapses and a high variety of typologies in open pit mines. The most common types of landslides are described below and illustrated in the following figure.

Although many types of landslides are included in the general term “slide”, the more restrictive use of the term refers only to landslides, where there is a different zone of weakness separating the landslide material from the more stable underlying material. . The two main types of landslides are rotational and translational. Rotational landslide: It is a landslide in which the rupture surface curves concavely upwards and the movement of the landslide is approximately rotational about an axis parallel to the ground surface and transverse through the landslide (fig.A). Translational Glide: In this type of glide, the detached mass moves along an approximately flat surface with little rotation or backward tilt (fig.B). A block slide is a translational slide in which the mobile mass consists of a single unit or a few closely related units that move downslope as a relatively coherent mass (fig.C).

LANDSLIDES: Landslides are sudden movements of masses of geological materials, such as rocks, that break off steep slopes or cliffs (fig.D). The separation occurs alongrange of discontinuities, such as fractures, and movement occurs by free fall, rebound, and rolling. Falls are strongly influenced by gravity, mechanical weathering, and the presence of pore water. Overturning: Overturning falls are distinguished by the forward rotation of one or more units about some pivot point, below the unit, under the actions of gravity and forces exerted by adjacent units or by fluids in the cracks ( fig.E).

FLOWS: There are five basic categories of flows that differ from each other in fundamental ways.

• Alluvium: is a form of rapid mass movement in which a combination of loose soil, rock, organic matter, air, and water is mobilized as a suspension flowing downslope (fig.F). They are usually caused by intense surface water flow, due to heavy rainfall or rapid snowmelt, which erodes and mobilizes loose soil or rock on steep slopes. They can also be generated from other types of landslides that occur on steep slopes and that reach the bottom of the valley or stream.

• avalanche of drags: it is a variety of alluvium, very fast or extremely fast (fig.G).

• land wash: Earthflows have a characteristic "hourglass" shape (fig.H). The material on the slope liquefies and ends up forming a depression. The flow itself is elongated and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and in saturated conditions. However, dry streams of granular material are also possible.

• mud pouring: A mudflow is a flow of soil consisting of material moist enough to flow rapidly and containing at least 50% sand, silt, and clay-sized particles. In some cases, for example in many journalistic chronicles, mud flows and alluviums are commonly known as "mud flows".

• Creep: The creep is an imperceptibly slow, constant and downward movement of the soil or rock that forms the slopes. The movement is caused by a shear stress sufficient to cause permanent deformation but too small to cause general failure. There are generally three types of creep: (1) seasonal, where the movement is within depth of the soil affected by seasonal changes in soil moisture and temperature; (2) continuous, where the shear stress continuously exceeds the resistance of the material; and (3) progressive, where slopes reach breaking point like other types of mass movements. Drag is observed by curved tree trunks, bent fences or retaining walls, leaning posts or fences, and small undulations or ridges on the ground (fig.I).

SIDE EXPANSIONS: Lateral expansions are distinctive because they tend to occur on very gentle slopes or flat terrain (fig. J). The dominant mode of movement is lateral expansion accompanied by shear or traction fractures. Breakage is caused by liquefaction, the process by which loose, cohesive, saturated sediments (usually sands and silts) transform from a solid to a liquefied state. When cohesive material, either bedrock or soil, rests on materials that liquefy, the upper units may fracture and expand, and then may shrink, translate, rotate, disintegrate, or liquefy and flow. The fracture starts suddenly in a small area and spreads rapidly.